Rigid gas permeable (RGP) lenses are manufactured from materials that exhibit a high degree of polarity, resulting in a strong interaction with proteins and other tear constituents that ultimately produce tenacious surface deposits. Current state of the art care systems combat this problem through the use of unpreserved abrasive cleaners that produce microscopic scratches which, in time, shorten the useful life of the lens. Some attempts have been made to competitively block surface deposition by so-called "conditioning" solutions, but this approach involves the use of cytotoxic preservatives and does not eliminate the need for the abrasive cleaner.
Proteolytic enzymes have been of marginal value in controlling surface deposition because their action is limited to proteinaceous material. Multifunctional esterases capable of lysing both proteins and lipids failed to significantly improve on the results obtained with their proteolytic counterparts and the consequences of their usage was a delayed, but persistent, surface deposition and premature loss of the lens.
Aside from the problem of ultimate surface contamination, the RGP lens wearer is also faced with an initial discomfort problem until the lens completely hydrates, at which time it displays its best wetting and consequently its greatest comfort. In order to ensure that this maximal comfort is maintained, it is essential that the wettability of the surface be maintained. Moreover, the capability of the lens to resist surface deposition is also directly related to the maintenance of its wettability. The current state of the art lens care systems do not maintain optimal wettability over long periods of time because they are passive systems formulated to deal with the result of the polymer's surface interactions rather than to eliminate its cause.
RGP lenses have the potential of providing an unsurpassed level of comfort for a rigid lens. Unfortunately, the wearer realizes this benefit for only a short period of time because the current passive RGP care systems are unable to maintain this property.
Initial treatment of new RGP lenses usually includes cleaning with an abrasive cleaner, after which the lens may be soaked in a viscous, polar solution, to purportedly interact with active sites on the lens surface and thereby block their interaction with contaminants. The failure of this system to achieve this result is evident in the fact that the abrasive cleaner must be used on a daily basis and even then, adjunctive products are frequently needed. "Conditioning" then must require abrading the surface as part of the process. Aside from the lack of efficacy of this system, it shortens the functional life of the lens thereby producing a financial loss for the wearer.
The sequence of a separate cleaner (generally abrasive), a separate rinse solution, a separate soak solution, re-rinsing again after soaking and a separate wetting solution and a separate "in-eye" re-wetting solution or a system of a separate abrasive cleaner and a combined soaking, conditioning solution and a separate "in-eye" re-wetting solution is the basis for all known contact lens systems of hygiene other than the present invention. There are several serious objections to this sequence of operations.
Cleansing is a manual procedure that requires rubbing the lens between the fingers or in the palm of the hand. Only a small volume of cleaner is used and the procedure ideally (but rarely) requires at least 1 minute. Regardless of the chemical composition of the cleaning solution, this is primarily a physical procedure that involves the interaction of friction induced by the rubbing and the surfactant properties of the solution. In some cases, the friction is enhanced by the suspension of abrasive particles in the cleaner.
Abrasives added to improve on the cleansing action of manual procedures may damage the lens either by producing microscopic scratches and/or changing the lens parameters. Incomplete rinsing of cleaners that contain suspended abrasives may result in harmful residues that induce corneal damage.
Physical cleansing is also ineffective against bacteria that form biofilms. The common species of bacteria that have been linked to ocular infections, namely, pseudomonas aeruginosa and serratia marcescens, are known to secrete a slime-like covering of their cell walls to protect against a hostile environment. These organisms grow in contact lens cases despite the presence of a preserved soaking solution and may even contaminate bottles containing the solutions.
The use of a second solution for soaking and disinfecting usually results in the utilization of preservatives that are limited in their biocidal activity as a result of the requirement that they be non-irritating to ocular tissues. This situation came about because the manufacturers wanted to limit the number of steps required for lens care, hoping to encourage compliance. It was common practice for patients to remove their lenses from the soaking solution and place them directly on their eye therefore necessitating that they not irritate the ocular tissues. When rinsing was prescribed, the wearers were encouraged to use a rewetting drop so as to "cushion" the eye from the initial impact of a solution that might tend to irritate it.
In order to achieve some measure of effective hygiene, the manual system usually evolved into the use of 3 or 4 separate products, a cleaner, a viscous soaking/disinfecting solution, an enzymatic cleaner and sometimes a rewetting or cushioning drop. This resulted in a complicated, time-consuming regimen that discouraged compliance and added to the cost of lens care.
Known and/or FDA approved cleaning and wetting solutions for RGP contact lenses utilize hydrophobic preservatives or disinfecting agents such as benzalkonium chloride, chlorhexidine or polyamino-propyl biguanide. These hydrophobic materials tend to reduce the wettability of RGP lenses, especially fluorinated RGP lenses, thereby making cleaning and wetting more difficult. A surfactant polymer may be added to such formulations specifically to attempt to overcome the effect of the hydrophobic preservative.
A need exists for an active RGP lens care system that deals with the causes of surface deposition and poor wetting without resorting to the use of abrasives, cytotoxic chemicals or enzymes, and without the use of preservatives that reduce the wettability of the lenses.
A need also exists for a new preservative system for contact lens solutions and over-the-counter and prescription drug ophthalmic solutions.